4145H steel, from the perspective of its alloy composition, belongs to low-alloy high-strength steel. In low-alloy structural steels, the addition of certain amounts of Mn, Cr, Mo, Si, and other alloy elements can effectively improve the hardness, toughness, ductility, and wear resistance of the structural steel. This type of steel not only has a relatively low cost but also can achieve high strength and hardness through simple quenching and tempering (QT) processes. It easily achieves a good balance between strength and ductility and is widely used in various structural components. The commonly used alloy elements can be classified based on their roles in the steel’s strengthening mechanisms: solid solution strengthening elements (Mn, Si, C, etc.), precipitation strengthening elements (Nb, V, Ti, etc.), and transformation strengthening elements (Mn, Mo, Si, etc.).
1. The Role of Element C:
Carbon is a fundamental element in steel and plays a significant role. In structural steels, on one hand, carbon is an important strengthening element. As a gap solid solution element, carbon contributes to a notable increase in solid solution strengthening, with its reinforcing effect increasing with higher carbon content. Additionally, carbon forms fine and dispersed alloy carbides with strong carbide-forming elements, resulting in dispersion strengthening and further enhancing strength. Higher carbon content leads to greater material hardness. On the other hand, as carbon content increases, the toughness of the steel decreases, and weldability deteriorates.
2. The Role of Element Cr:
Chromium enhances the hardenability of steel and has a secondary hardening effect. It improves the hardness and wear resistance of carbon compounds without embrittling the steel. When chromium exceeds 12%, it imparts excellent high-temperature oxidation resistance and resistance to oxidative corrosion to the steel, as well as increases its thermal strength. Chromium is a primary alloying element in stainless steels, acid-resistant steels, and heat-resistant steels. Chromium also increases the strength and hardness of carbon steels in their rolled state while reducing elongation and reduction of area. When chromium content exceeds 15%, strength and hardness decrease, while elongation and reduction of area increase accordingly. Parts made of chromium-containing steel can achieve high surface finish quality after grinding.
3. The Role of Element Mo:
Molybdenum is an important alloying element. In steel, molybdenum improves quenchability and thermal strength, prevents temper embrittlement, increases residual magnetism and coercivity, and enhances corrosion resistance in certain media. In quenched and tempered steels, molybdenum ensures deeper and more uniform hardening of larger cross-section parts, improves the steel’s resistance to tempering or tempering stability, allowing parts to be tempered at higher temperatures. This effectively eliminates (or reduces) residual stress and improves plasticity.
4. The Role of Element Mn:
Manganese serves as an excellent deoxidizer and desulfurizer. Steels generally contain a certain amount of manganese, which eliminates or reduces sulfur-induced hot brittleness in steel, thereby improving its hot working properties. Manganese forms solid solutions with iron, increasing the hardness and strength of ferrite and austenite in steel. It is also a carbide-forming element that replaces part of the iron atoms in cementite. Manganese lowers the critical transformation temperature in steel, refining pearlite and indirectly increasing the strength of pearlitic steel.
5. The Role of Element V:
Vanadium is added to some 4145H steels. Vanadium has a strong affinity with carbon, nitrogen, and oxygen, forming stable compounds with them. These compounds contribute to grain refinement and precipitation strengthening in the steel.
Post time: Feb-14-2025
